Here's why:
* Prepositional Phrases consist of a preposition followed by its object. Examples include:
* in the house
* on the table
* with a smile
* "For example" acts as a conjunction, introducing an example or illustration. It's similar in function to phrases like "such as" or "for instance".
In context:
"I like to eat fruits, for example, apples and bananas."
Here, "for example" acts as a conjunction, not a prepositional phrase.